1. Field
Embodiments of the invention relate generally to a nonvolatile semiconductor memory device.
2. Background Art
Collectively patterned three dimensionally stacked memory cells have been proposed to increase the memory capacities of nonvolatile semiconductor memory devices (memory) (for example, refer to JP-A 2007-266143 (Kokai)). According to such methods, it is possible to suppress cost increases because a stacked memory can be collectively formed regardless of the number of stacks.
In such a collectively patterned three dimensionally stacked memory, insulating films are alternately stacked with electrode films (forming word lines) to form a stacked unit; and through-holes are collectively made in the stacked unit. A charge storage layer (a memory layer) is formed on the side faces of the through-holes; and silicon is filled into the interiors of the through-holes to form silicon pillars. A tunneling insulating film is provided between the charge storage layer and the silicon pillars; and a blocking insulating layer is provided between the charge storage layer and the electrode films. Thereby, memory cells made of, for example, MONOS (Metal Oxide Nitride Oxide Semiconductor) transistors are formed at the intersections between the silicon pillars and the electrode films.
Further, a silicon pillar having a U-shaped configuration can be formed by using a connection portion provided on the silicon substrate side to connect two of the through-holes. In other words, a through-hole having a U-shaped configuration is made; the blocking insulating layer, the charge storage layer, and the tunneling insulating film are formed on the side wall thereof; and silicon is filled into the remaining space to form a memory string made of the silicon pillar having the U-shaped structure.